| Abstract | Changes in the dimensions and heat content of hydrated cement specimens were determined as a function of temperature and concentration of deicing agent in cooling- warming cycles between +15 degrees C and -70 degrees C. The concentration of the polar deicer (NaCl) solution varied from 0 to 26% and that of the nonpolar (urea) solution from 0 to 40%. The w/c raios were 0.4, 0.6, and 0.8 plain and 0. 5 air-entrained. Experiments were also conducted to clarify the effect of cooling rate and sample size. The observations can be explained by the mechanism previously proposed for phase transitions of adsorbates. In the presence of salts, freezing and melting of liquid exuded from the pores on cooling proceed according to the bulk phase diagram, producing double peaks in the thermograms except at extreme concentrations. The detrimental effect of deicers is attributed mainly to the high degree of saturation, a consequence of the low vapor pressure of the solutions. A beneficial aspect is the widening of the temperature range in which transitions occur. These opposing effects result in the worst conditions at a low deicer concentration (5% NaCl) and optimum conditions at a moderately high concentration (13% NaCl). Since the effect of deicers is physical, it should be common to all chemicals. Air entrainment, although beneficial in most circumstances, can be detrimental. The best protection against "salt scaling" appears to be reduction of porosity. |
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